Qualitative and Quantitative Methods for Isolation and Characterization of Lignin-Modifying Enzymes Secreted by Microorganisms

Lignin is a polyphenolic biopolymer synthesized by plants, for providing strength and rigidity to the plant cellular structure. It is closely associated with other plant polysaccharides in the cell wall such as cellulose and hemicellulose, constituting the most abundant biopolymer on the earth's surface. However, the complete utilization of it is being explored for the past few years. Various research groups around the world are trying to replace conventional fuels with the second-generation biofuels from lignocellulose. Several physical, chemical, and biological conversion methods have been developed for the separation and utilization of this biomass, as a result of which biological methods for lignocellulose conversion are considered to be cheap and environment-friendly. Microorganisms, especially fungi and bacteria, have been able to degrade the lignocellulose network and convert it to commercially important biofuels by secreting several intra- and extra-cellular enzymes. In the past few years, research has been conducted to isolate efficient lignin-degrading microorganisms, as separation of lignin from cellulosic biomass is considered as a major hurdle in biofuel and pulping industries. In this article, we extensively discuss different small- and large-scale methods developed for the isolation and characterization of lignin-degrading microorganisms. We have also comprehensively discussed about the qualitative and quantitative methods for the identification and characterization of the lignin-degrading and lignin-degrading auxiliary enzymes by comparing different methods based on their efficiency. This review can be used as a primer for understanding and selecting the most efficient method for isolation and characterization of lignin-degrading microorganisms and their enzymes.